Slot machine executing free game according to game outcome of sub game

ABSTRACT

A slot machine executes a sub game during a base game, and executes a free game in response to a game outcome of the executed sub game. Specifically, the slot machine is configured to execute the sub game different from the base game during the base game when symbols arranged on a main liquid crystal panel during the base game forms a combination in which three “CHANCE” symbols are arranged on a payline. Moreover, the slot machine is configured to execute the free game by switching from the base game to the free game when the player satisfies a winning condition a predetermined number of times or more in the sub game.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a slot machine that executes a sub gameduring a base game and executes a free game in response to a gameoutcome of the executed sub game.

2. Description of the Related Art

A conventional slot machine that is one type of gaming machine isconfigured: to start a game when gaming values such as coins areinserted into the gaming machine; to display columns of symbols in ascrolling manner on a predetermined area of the gaming machine, then tostop scrolling and display the symbols after a predetermined time haselapsed, and to award a prize based on the combination of the stoppedsymbols. Moreover, whether or not a combination for awarding a prize isestablished is generally determined according to whether or not apredetermined number of symbols of one kind (for example, “CHERRY” or“7”) are arranged on a preset payline. In addition, heretofore, a prizehas been also awarded based on a combination not related to a payline.For example, U.S. Pat. No. 6,334,612 discloses a slot machine thatdisplays a total of 15 symbols of 3×5 by using video reels or mechanicalreels. In this slot machine, the reels are rotated once a game starts,and symbols arranged in a vertical direction in each column startscrolling in synchronization with the rotation of the reels. Then, whenthe reels stop rotating after a predetermined time has elapsed, threestopped symbols are displayed in each column. If the displayed symbolsstop in a combination including a predetermined number of symbols ormore of one kind, a prize is awarded.

Here, a plenty of conventional slot machines are known, each of whichexecutes two kinds of games, that is, a base game and a free game. Thebase game is a game executed with a consumption of gaming values (coins,credits or the like) equivalent to a bet amount. On the other hand, thefree game is a game executed without requiring gaming values equivalentto a bet amount to be consumed. The game is switched from the base gameto the free game in a case where a predetermined condition is satisfied,such as a case where a predetermined symbol is stopped and displayed.Then, the game is switched from the free game to the base game in a casewhere a predetermined condition is satisfied, such as a case where thefree game has been already executed a predetermined number of times.

Here, a player desires the slot machine to execute the free game thatprovides a higher probability of obtaining a large number of gamingvalues. In the conventional slot machine, therefore, the player has beenobliged to be kept waiting for a start of the free game by repeating thebase game, and accordingly, to accept such a monotonous play style.

The present invention provides a slot machine providing enhancedentertainment by variously changing a condition for starting a free gamein such a way that a sub game different from a base game is executedduring the base game, and that the free game is then started in responseto a game outcome of the sub game.

SUMMARY OF THE INVENTION

A slot machine of the first aspect of the present invention includes adisplay adapted to have multiple symbols arranged on the display, a betreceiving button configured to receive a bet operation, and a controllerconfigured to execute a base game and a free game by switching thesegames under predetermined conditions. Here, the base game is designed tostart in response to a consumption of gaming values equivalent to a betamount received by the bet receiving button, and to award a prize whenthe plurality of symbols arranged on the display forms a predeterminedcombination, while the free game is designed to start without consumingany gaming value, and to award a prize when the plurality of symbolsarranged on the display forms a predetermined combination. In addition,the controller is configured to execute a sub game that is differentfrom the base game, in the base game, and switch the game mode from thebase game to the free game in response to a game outcome of the subgame.

The slot machine of the first aspect of the present invention having theaforementioned configuration starts the free game in response to thegame outcome of the sub game that is different from the base game. Forthis reason, the condition for starting the free game does not have tobe limitative only to a game outcome of the base game, and thus, thecondition for starting the free game can be variously changed. Inaddition, a player is allowed to play the sub game in addition to thebase game, thus avoiding monotony of the game. This enables the playerto continue playing the game for a long time. Thus, the entertainment ofthe game is enhanced.

A slot machine of the second aspect of the present invention includes adisplay adapted to have a plurality of symbols arranged on the display,a bet receiving button configured to receive a bet operation, and acontroller configured to execute a base game and a free game byswitching these games under predetermined conditions. Here, the basegame is designed to start in response to a consumption of gaming valuesequivalent to a bet amount received by the bet receiving button, and toaward a prize when the plurality of symbols arranged on the displayforms a predetermined combination, while the free game is designed tostart without requiring any gaming value to be consumed, and to award aprize when the plurality of symbols arranged on the display forms apredetermined combination. The controller is configured to execute a subgame that is different from the base game during the base game, todetermine whether a player satisfies a winning condition a predeterminednumber of times of more in the sub game, and to switch the game modefrom the base game to the free game when the controller determines thatthe player satisfies the winning condition the predetermined number oftimes or more.

The slot machine of the second aspect having the aforementionedconfiguration starts the free game when the controller determines that aplayer satisfies the winning condition a predetermined number of timesor more in the sub game. Accordingly, with the progress of the sub game,the slot machine of the second aspect can promote player's expectationsfor the start of the free game. Hence, the entertainment of the game isenhanced.

A slot machine of the third aspect of the present invention includes adisplay adapted to have a plurality of symbols arranged on the display,a bet receiving button configured to receive a bet operation, and acontroller configured to execute a base game and a free game byswitching these games under predetermined conditions. The base game isdesigned to start in response to a consumption of gaming valuesequivalent to a bet amount received by the bet receiving button, and toaward a prize when the plurality of symbols arranged on the displayforms a predetermined combination, while the free games are designed tostart without requiring any gaming value to be consumed, and to award aprize when the plurality of symbols arranged on the display forms apredetermined combination. The controller is configured to execute a subgame different from the base game when a predetermined combinationincluding a particular symbol is arranged on the display during the basegame, to determine whether or not a player satisfies a winning conditionfor the sub game a predetermined number of times or more, and then, toswitch the game mode from the base game to the free game when thecontroller determines that the player satisfies the winning conditionthe predetermined number of times or more.

The third slot machine of the third aspect having the aforementionedconfiguration executes the sub game when the combination including theparticular symbol is arranged on the display in the base game, and then,starts the free game when the controller determines that the playersatisfies the winning condition the predetermined number of times ormore in the thus executed sub game. This promotes player's expectationsfor an event where the particular symbol is arranged in the base game,and also promotes player's expectations for the start of the free gamewith the progress of the sub game. Thus, the entertainment of the gameis enhanced.

A slot machine of the fourth aspect of the present invention includesthe controller of the slot machine of the first aspect. The controllerof the slot machine of the fourth aspect is configured to execute thesub game different from the base game when a combination including aparticular symbol is arranged on the display in the base game.

Since the slot machine of the fourth aspect having the aforementionedconfiguration executes the sub game when the combination including theparticular symbol is arranged on the display in the base game, player'sexpectations for an event where the particular symbol is arranged in thebase game are enhanced.

A slot machine of the fifth aspect of the present invention includes thecontroller of the first slot machine. The controller of the fifth slotmachine is configured to select one sub game among multiple types of subgames when a predetermined condition is satisfied during the base game,and then to switch the game mode from the base game to the free game inresponse to a game outcome of the selected sub game.

The slot machine of the fifth aspect having the aforementionedconfiguration has the multiple types of sub games, and the executed subgame is changed for every session of the sub game, thus avoidingmonotony of the game. In addition, the condition for switching to thefree game can also be changed for every session of the sub game, so thatthe entertainment of the game is enhanced.

A slot machine of the first aspect of the present invention has the subgame of the first slot machine including multiple types of sub games.The multiple types of sub games have different challenge levels fromeach other, the challenge levels imposed on a player to satisfy winningconditions of the respective sub games.

In the slot machine of the sixth aspect having the aforementionedconfiguration, since the multiple types of sub games employ thedifferent challenge levels to be imposed on the player to satisfy therespective winning conditions, and thereby, the player feels a differentlevel of expectations, depending on the type of the executed sub game,for switching to the free game. Hence, the slot machine of the sixthaspect provides the player with such a different level of expectationsdepending on the type of the selected sub game, thereby enhancing theentertainment of the game. Furthermore, the slot machine of the sixthaspect is capable of providing the game that lets even a player with apoor gaming technique enjoy playing sufficiently and prevents a playerwith a good gaming technique from getting bored.

A slot machine of the seventh aspect of the present invention includesthe controller of the first slot machine of the first aspect. Thecontroller of the slot machine of the seventh aspect is configured todetermine the number of times of the free game to be executedsubsequently to the sub game, on the basis of a game outcome of the subgame.

Since the slot machine of the seventh aspect having the aforementionedconfiguration determines the number of times of the free game to beexecuted subsequently to the sub game, on the basis of a game outcome ofthe sub game, player's expectations for acquiring a large amount ofgaming values in the subsequently-executed free game changes accordingto the game outcome of the executed sub game. Thereby, the entertainmentof the game is enhanced.

Since the slot machine according to the present invention starts thefree game in response to the game outcome of the sub game different fromthe base game, the condition for starting the free game does not have tobe limitative only to the game outcome of the base game, but can bevariously changed. Moreover, the player is allowed to play the sub gamein addition to the base game. As a result, the monotony of the game isavoided, and this enables the player to continue playing the game for along time. Thus, the entertainment of the game is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a feature of a slot machine according to apresent embodiment.

FIG. 2 is a perspective view showing an external appearance of the slotmachine according to this embodiment.

FIG. 3 is a schematic diagram showing symbol columns drawn on reel bandsof the respective reels.

FIG. 4 is a block diagram showing an internal configuration of the slotmachine according to this embodiment.

FIG. 5 is a block diagram showing an internal configuration especiallyof a sub-control board of the slot machine according to this embodiment.

FIG. 6 is a diagram showing a game screen displayed on a main liquidcrystal panel during an execution of the base game.

FIG. 7 is a diagram showing a game screen displayed on the main liquidcrystal panel during the execution of the base game.

FIG. 8 is a payout table showing winning combinations and payout amountsfor the respective winning conditions in a case where the base game anda free game are executed by using the reels.

FIG. 9 is a diagram showing a game screen displayed on the main liquidcrystal panel during an execution of the sub game.

FIG. 10 is a diagram showing a game screen displayed on the main liquidcrystal panel during the execution of the sub game.

FIG. 11 is a diagram showing a game screen displayed on the main liquidcrystal panel during the execution of the sub game.

FIG. 12 is a diagram showing a list of sub games executed in the slotmachine according to this embodiment.

FIG. 13 is a flowchart of a main control processing program in the slotmachine according to this embodiment.

FIG. 14 is a flowchart of a main game processing program in the slotmachine according to this embodiment.

FIG. 15 is a flowchart of a sub game processing program in the slotmachine according to this embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, an exemplary embodiment of a slot machine according to thepresent invention will be described in detail with referring to thedrawings. Here, a slot machine according to the following embodiment isa so-called hybrid-type slot machine being provided with a knowntransparent liquid crystal panel arranged in front of multiplerotatably-supported mechanical reels and executing games by making theliquid crystal panel transparent to display the images of varioussymbols drawn on the outer peripheral surfaces of the mechanical reels.

In addition, a feature of the slot machine according to the presentinvention is that the slot machine not only executes a base game and afree game but also a sub game. More precisely, the base game is onewhich a player plays by consuming gaming values equivalent to a betamount, the free game is one which the player plays without consumingany gaming value, and the sub game is different from the base game andis executed during the base game. Moreover, another feature of the slotmachine is that the base game is switched to the free game not inresponse to a game outcome of the base game, but in response to a gameoutcome of the sub game.

For example, FIG. 1 shows a case where the present invention is appliedto a slot machine including three columns of reels 5 to 7. When the basegame is started in the slot machine, each of the reels 5 to 7 startsrotating, and scrolling symbol columns are displayed. Then, after apredetermined time has elapsed, the reels 5 to 7 stop rotating one byone from the left-hand side, symbols of up to 9 are displayed in asymbol display area as shown in FIG. 1(1). Here, when three “CHANCE”symbols are stopped on a payline L altogether, the sub game is startedduring the base game as shown in FIG. 1(2). Incidentally, there aremultiple types of sub games, and one of the sub games to be executed isselected every time before a new session of the sub game is started. InFIG. 1, a description is given as to a case where a subgame of picking awinning card among from multiple shuffled cards is selected. In the subgame, multiple cards including a “winning card” and “losing cards” aredisplayed on a main liquid crystal panel 11B, and the cards areshuffled. Thereafter, if a player picks the “wining card” three times inthe sub game as shown in FIG. 1(3), which is a winning condition for theplayer, the sub game is terminated and the game mode is switched fromthe base game to the free game. Thus, the free game is started as shownin FIG. 1(4). The number of times in a case where the free game is to beexecuted at this time changes depending on the number of picked cardsneeded until the condition that the “winning card” is picked three timesis satisfied. If the condition is satisfied by three trials, fourtrials, and five trials, the player is allowed to play the free game 20,10 and 5 times, respectively. On the other hand, if the player picks the“losing card” three times during the sub game, which is a losingcondition for the player, the sub game is terminated and the base gameis continuously executed.

First of all, a schematic configuration of a slot machine 1 according tothis embodiment will be described based on FIG. 2. FIG. 2 is aperspective view of an external appearance of the slot machine 1according to this embodiment. The slot machine 1 according to thisembodiment is an upright type slot machine installed in a game arcadesuch as a casino, and includes a cabinet 2, a main door 3 provided inthe front surface of the cabinet 2, and a topper announcement effectdevice 4 arranged above the cabinet 2.

The cabinet 2 is intended for housing electric or mechanical componentsfor executing predetermined game modes. Three of a left reel 5, a middlereel 6 and a right reel 7 are rotatably provided to the inside of thecabinet 2. A symbol column (see FIG. 3) consisting of 22 symbols isdrawn on the outer peripheral surface of each of the reels 5 to 7. Inaddition, the main liquid crystal panel 11B provided to the main door 3is arranged in front of the reels 5 to 7.

The main door 3 includes, as a display unit 10 for displayinginformation on the game, an upper display unit 10A, a variable displayunit 10B on the middle side, and a lower display unit 10C. The upperdisplay unit 10A is provided with an upper liquid crystal panel 11Aarranged above the variable display unit 10B. Thus, for example, aneffect image, a presentation of the game content, and an explanation ofgame rules or the like are displayed on the upper liquid crystal panel11A. The lower display unit 10C includes a plastic panel 11C arrangedbelow the variable display unit 10B and having an image printed thereon.Then, this plastic panel 11C is illuminated with a backlight.

Moreover, the variable display unit 10B for displaying the situation ofexecuting the game includes the main liquid crystal panel 11Bconstituted of a known transparent liquid crystal panel fixed to themain door 3. Here, three display windows 15, 16 and 17 are formed in themain liquid crystal panel 11B, and allow the side behind the main liquidcrystal panel 11B to be viewed. The symbols drawn on the reels 5 to 7are made visible by making the display windows 15, 16 and 17transparent. In addition, one payline L horizontally crossing a symboldisplay area corresponding to all the reels 5 to 7 is displayed on themain liquid crystal panel 11B in the variable display unit 10B. Thepayline L is used to define a combination of symbols. If a combinationof symbols stopped and displayed on the payline L is a predeterminedcombination, a payout amount corresponding to the combination and a betcredit amount (bet amount) is provided. Incidentally, five reels may beemployed instead of the three reels, and the number of displayed symbolsis not limitative to 9.

Moreover, the front surface of the main liquid crystal panel 11B isprovided with a touch panel 18, and a player can input variousinstructions by operating the touch panel 18. In the slot machine 1according to this embodiment, the touch panel 18 is used by the playerto select one of choices (for example, cards) displayed in the sub gamewhich will be described later.

Furthermore, a payout amount display portion 19 and a credit amountdisplay potion 20 are provided on the right lower side of the variabledisplay unit 10B. The payout amount display portion 19 displays, as apayout amount, a payout amount provided in the base game if acombination of symbols stopped and displayed on the payline L is apredetermined combination or a cumulative payout amount obtained in thefree game. The credit amount display potion 20 displays a credit amountcurrently owned by the player.

An operation table 25 extending forward is provided between the variabledisplay unit 10B and the lower display unit 10C in the front surface ofthe cabinet 2. On the operation table 25, various operation buttons 26such as a BET button, a correct button, a start button and a CASHOUTbutton are arranged as an operation area for making instructions for anexecution of the game. In addition, a coin insertion slot 27 forinserting coins into the cabinet 2 and a bill insertion slot 28 forinserting bills in the cabinet 2 are provided on the operation table 25.

Incidentally, for the slot machine 1 according to this embodiment,coins, bills and equivalent electronic value information (credit) areused as the game gaming values. However, the game gaming values usablein the present invention are not limitative thereto, but also includemedals, tokens, e-money and tickets, for example.

A coin tray 29 receiving coins provided by a hopper is provided to thelowest portion of the cabinet 2. In addition, a lighting unit 30 isdisposed around the cabinet 2 of the slot machine 1, and lights up in apredetermined lighting manner in the case of winning or during the freegame. A speaker 31 outputting sounds is also provided at each side ofthe cabinet 2.

Moreover, the slot machine 1 includes the topper announcement effectdevice 4 above the cabinet 2. This topper announcement effect device 4is in a rectangular board shape, and is disposed substantially inparallel with the upper liquid crystal panel 11A of the upper displayunit 10A.

Subsequently, based on FIG. 3, a description will be furnished as to thesymbols drawn on the left reel 5, the middle reel 6 and the right reel7, and rearranged while scrolling in the respective display windows 15to 17 of the main liquid crystal panel 11B through during executions ofthe base game and the free game. FIG. 3 is a schematic diagram showingsymbol columns drawn on the reel belts of the left reel 5, the middlereel 6 and the right reel 7.

22 symbols are drawn on each of the reel belts of the reels 5 to 7. Eachof the symbol columns is constituted of a configuration of symbols“CHANCE”, “BLUE7”, “BELL”, “APPLE”, “CHERRY”, “STRAWBERRY”, “PLUM” and“ORANGE”. Then, predetermined kinds of symbols are arranged in apredetermined order in each of the symbol columns.

In this regard, when three symbols of each of “BLUE7”, “BELL”, “APPLE”,“CHERRY”, “STRAWBERRY”, “PLUM” and “ORANGE” are rearranged on thepayline L on the main liquid crystal panel 11B, a player is providedwith a predetermined payout amount (see FIG. 8). In addition, when evenone or two symbols of each of “CHERRY” and “ORANGE” are rearranged onthe payline L on the main liquid crystal panel 11B, a player is providedwith a predetermined payout amount predetermined corresponding to thenumber of symbols (see FIG. 8).

Moreover, when three symbols “CHANCE” are rearranged on the payline L onthe main liquid crystal panel 11B, a predetermined payout is provided tothe player and the sub game is executed in parallel with the base game.Incidentally, symbol numbers are assigned in descending order to therespective symbols constituting each of the symbol columns shown in FIG.3.

Next, an internal configuration of the aforementioned slot machine 1will be described with referring to FIGS. 4 and 5. FIG. 4 is a blockdiagram showing an entire internal configuration of the slot machine 1.As shown in FIG. 4, the slot machine 1 is constituted of multiplecomponents including, as a main component, a main control board 71having a controller 41 for executing a control program (FIGS. 13 to 15),which will be described later. The main control board 71 includes thecontroller 41, a random number generation circuit 45, a sampling circuit46, a clock pulse generation circuit 47, a frequency divider 48, alighting effect drive circuit 61, a hopper drive circuit 63, a payoutcompletion signal circuit 65 and a display-unit drive circuit 67.

The controller 41 includes a main CPU 42, a RAM 43 and a ROM 44. Themain CPU 42 operates in accordance with programs stored in the ROM 44and controls the operations of the entire slot machine 1 by inputtingand outputting signals from and to the other components through an I/Oport 49. The RAM 43 stores therein data and programs used in theoperations of the main CPU 42. For instance, in the RAM 43, randomnumber values sampled by the sampling circuit 46, which will bedescribed later, are temporarily stored after the game has started, andthe code numbers of the respective reels 5 to 7 and the symbol numbersare also stored. The ROM 44 stores therein the programs executed by themain CPU 42 and permanent data.

In particular, the programs stored in the ROM 44 include a game programand a game system program (hereinafter, referred to as a game programand the like). Moreover, the game program includes first to thirdlottery programs described below.

The first lottery program is a program for determining one of the codenumbers for each of the reels 5 to 7, and the determined code numbercorresponds to a symbol to be rearranged on the payline L in the mainliquid crystal panel 11B. This lottery program includes symbol weightingdata corresponding to multiple kinds of payout rates (for example, 80%,84% and 88%). The symbol weighting data is data indicative ofcorrespondence between each of the code numbers of the three reels 5 to7, and one or more random numbers within a predetermined range ofnumeric values (0 to 255). In other words, a single code number isassociated with one or more random numbers, each of which corresponds toone of the payout rates. After a predetermined random number isextracted by lottery, a symbol eventually specified from the extractedrandom number is rearranged on the payline L in the main liquid crystalpanel 11B. Note that the lottery program for determining symbols to bearranged may use weighting data in which a predetermined range ofnumeric values is associated with a prize awarded to a player. In thiscase, first, a prize to be awarded to a player is determined by lotteryin accordance with the lottery program. Then, a combination of symbolssatisfying the determined prize is selected by the main CPU 42.

The second lottery program is a program for determining one of the subgames to be executed when the sub game is about to be executed. Thislottery program includes a sub game selection table corresponding toeach of multiple types of sub games (for example, a “shuffle card game”,a “spot the difference”, a “horse racing game”, a “memory”, a “quiz” andthe like). The sub game selection table is data indicative ofcorrespondence between each of the sub games and one or more randomnumbers within a predetermine range of numeric values (0 to 255). Inshort, by extracting one of the random numbers by lottery, the subgamespecified from the random number is determined as the subgame to beexecuted.

The third lottery program is a program for determining various kinds ofparameters needed to execute each type of the sub games. For example,when the “shuffle card game” or “memory” is to be executed as the subgame, kinds of cards to be arranged on the main liquid crystal panel 11Bare determined. Instead, when the “spot the difference” is to beexecuted as the sub game, two images of characters and scenery to bedisplayed on the main liquid crystal panel 11B are determined as atarget for “spot the difference”. Alternatively, when the “horse racinggame” is to be executed as the sub game, a horse to win is determined.Moreover, when the “quiz” is to be executed as the sub game, questionsto be given and choices of answers are determined.

The random number generation circuit 45 operates in accordance withinstructions from the main CPU 42, and generates a predetermined rangeof random numbers. The sampling circuit 46 extracts a predetermined oneof the random numbers generated by the random number generation circuit45 in accordance with an instruction from the main CPU 42 and inputs theextracted random number to the main CPU 42. The clock pulse generationcircuit 47 generates reference clocks for operating the main CPU 42, andthe frequency divider 48 inputs, to the main CPU 42, the signal obtainedby dividing the frequency of the reference clocks into a predeterminedfrequency.

In addition, a reel drive unit 50 is connected to the main control board71. This reel drive unit 50 includes a reel position detecting circuit51 for detecting the position of each of the reels 5 to 7, and a motordrive circuit 52 for inputting drive signals to motors M1, M2 and M3 forrotating the respective reels 5 to 7. The motors M1, M2 and M3 operatein response to an input of the drive signals from the motor drivecircuit 52, rotate the respective reels 5 to 7, and then, stop the reels5 to 7 at desired positions.

Moreover, a touch panel 18 is connected to the main control board 71,and is disposed in front of the main liquid crystal panel 11B. Thistouch panel 18 is capable of identifying a coordinate position of a parttouched by a player, and that of determining, by using the identifiedcoordinate position information, where the player touches and in whichdirection the touched part moves. Then, a signal corresponding to thedetermination is inputted to the main CPU 42 through the I/O port 49.

The operation buttons 26 including the start button, the correct button,the BET button and the like, for making an instruction for an executionof the game, are connected to the main control board 71. Then, a signalresponsive to a press of one of the buttons is inputted to the main CPU42 through the I/O port 49.

The lighting effect drive circuit 61 outputs effect signals for causingthe foregoing lighting unit 30 and topper announcement effect device 4to produce lighting effects. The topper announcement effect device 4 isserially connected to a lighting effect drive circuit 61 through thelighting unit 30.

A hopper drive circuit 63 drives a hopper 64 under control of the mainCPU 42. Thereby, the hopper 64 pays out coins to the coin tray 29 byperforming an operation for paying out coins. A payout completion signalcircuit 65 receives value data on the number of coins from a coindetection unit 66 that is connected to the payout completion signalcircuit 65. When the number of paid-out coins reaches a set number ofcoins, the payout completion signal circuit 65 inputs, to the main CPU42, a signal notifying the main CPU 42 of the completion of payout ofcoins. The coin detection unit 66 counts the number of coins provided bythe hopper 64, and inputs the value data on the counted number of coinsto the payout completion signal circuit 65. The display-unit drivecircuit 67 controls display operations of various display portions suchas the payout amount display portion 19 and the credit amount displaypotion 20.

Moreover, a sub-control board 72 is connected to the main control board71. As shown in FIG. 5, the sub-control board 72 receives commands fromthe main control board 71, and controls the displays of the upper liquidcrystal panel 11A of the upper display unit 10A and the main liquidcrystal panel 11B of the variable display unit 10B, as well as the soundoutput from the speaker 31. This sub-control board 72 is configured on acircuit board that is different from the circuit board constituting themain control board 71. The sub-control board 72 includes a microcomputer(hereinafter, referred to as a “sub-microcomputer”) 73, as a maincomponent, and also includes a sound source IC 78, a power amplifier 79,and an image control circuit 81. The sound source IC 78 controls thesound outputted from the speaker 31, the power amplifier 79 is employedas an amplifier, and the image control circuit 81 operates as a displaycontrol unit for the upper liquid crystal panel 11A and the main liquidcrystal panel 11B.

The sub-micro computer 73 includes a sub CPU 74 that performs controloperations in accordance with control commands transmitted from the maincontrol board 71, as well as a program ROM 75 and a work RAM 76 asstorages, and I/O ports 77 and 80. The sub-control board 72 is notprovided with a clock pulse generation circuit, a frequency divider, arandom number generation circuit or a sampling circuit, but isconfigured to execute random number sampling on an operation program ofthe sub CPU 74. The program ROM 75 stores therein a control programexecuted by the sub CPU 74. The work RAM 76 is configured as a temporalmemory used when the sub CPU 74 executes the control program.

The image control circuit 81 includes an image control CPU 82, an imagecontrol work RAM 83, an image control program ROM 84, an image ROM 86, avideo RAM 87 and an image control IC 88. In accordance with an imagecontrol program stored in the image control program ROM 84, the imagecontrol CPU 82 determines images to be displayed on the upper liquidcrystal panel 11A and the main liquid crystal panel 11B.

The image control program ROM 84 stores therein the image controlprogram for the displays on the upper liquid crystal panel 11A and themain liquid crystal panel 11B, and various selection tables. The imagecontrol work RAM 83 is configured as a temporal memory used when theimage control CPU 82 executes the image control program. The imagecontrol IC 88 forms images corresponding to the content determined bythe image control CPU 82, and outputs the images to the upper liquidcrystal panel 11A and the main liquid crystal panel 11B.

The image ROM 86 stores therein dot data for forming images. The videoRAM 87 operates as a temporal memory used when the image control IC 88forms the images.

Next, a description will be given as to the base game, the free game andthe sub game executed in the slot machine 1 having the aforementionedconfiguration. First of all, the base game is explained. The base gameis a slot game that causes the reels 5 to 7 to rearrange a particularcombination of symbols on the payline L in the main liquid crystal panel11B. Specifically, when the player sets the bet amount by operating theoperation buttons 26 and depresses the start button, the reels 5 to 7start rotating. As a result, as shown in FIG. 6, the symbol columnsdrawn on the reel belts of the respective reels 5 to 7 are displayedthrough the display windows 15 to 17 in the transparent state, whilescrolling from the upper side to the lower side. Then, after apredetermined time has elapsed, the reels 5 to 7 automatically stop on aone-by-one basis in a predetermined order. With this stop, as shown inFIG. 7, part of the symbol columns drawn on the reel belts of therespective reels 5 to 7 (three symbols for each reel, that is, ninesymbols 91 in total) are rearranged and displayed on the main liquidcrystal panel 11B through the display windows 15 to 17 in thetransparent state. Here, as to the base game, various kinds of winningcombinations each are predetermined as one of combinations of symbolsthat are rearranged on the main liquid crystal panel 11B. Thus, whenthree symbols rearranged on the payline L in the main liquid crystalpanel 11B form a combination corresponding to one of the winningcombinations, the player is provided with a credit amount obtained bymultiplying a payout amount corresponding to the formed winningcombination by the bet amount.

On the other hand, the free game executed in the slot machine 1 is agame executed by switching from the base game if a player satisfies awinning condition three times in the sub game, which will be describedlater. Here, the number of times of the free game is determined based ona game outcome of the sub game. Then, after the free game issuccessively executed the determined number of times, the free game isterminated and the game mode is switched to the base game again. Notethat the procedure of the free game is the same as the base game exceptfor in that the free game does not require any gaming value (credit)corresponding to a bet amount to be spent at a time of starting thegame, and in that the free game is automatically and successivelyexecuted without requiring the player to operate the operation buttons26. Accordingly, the detailed description of the procedure is omittedhere.

Next, with reference to FIG. 8, a description will be furnished as towining combinations and the respective payout amounts in a case wherethe base game and the free game are executed by using the reels 5 to 7in the slot machine 1 according to this embodiment. FIG. 8 is a payouttable indicating wining combinations and payout amounts of therespective wining combinations in a case where the base game or the freegame is executed by using the reels 5 to 7.

Here, the payout amounts shown in FIG. 8 are payout amounts where a betamount is “1”. Accordingly, when a bet amount is “1”, the payout amountexactly shown in FIG. 8 is provided. When a bet amount is “2” or more, apayout amount obtained by multiplying the bet amount by the payoutamount shown in FIG. 8 is provided. Note that the bet amount used duringthe free game is determined to be one equal to the bet amount in thebase game immediately before the start of the free game.

Thus, when three “CHANCE” symbols are rearranged on the payline L in themain liquid crystal panel 11B, a payout amount obtained by multiplyingthe bet amount by 10 credits is provided. Moreover, if during the basegame, the player wins a start trigger for the sub game and thereby thesub game is executed in parallel with the base game. Incidentally, ifthe “CHANCE” symbols are rearranged during the free game, only a payoutamount obtained by multiplying the bet amount by 10 credits is provided.

Instead, when three “BLUE7” symbols are rearranged on the payline L inthe main liquid crystal panel 11B, a payout amount obtained bymultiplying the bet amount by 10 credits is provided. When three “BELL”symbols are rearranged on the payline L in the main liquid crystal panel11B, a payout amount obtained by multiplying the bet amount by 8 creditsis provided. Similarly, a payout amount is set for each of the winningcombinations shown in FIG. 8. However, when a combination composed ofthree symbols rearranged on the payline L in the main liquid crystalpanel 11B does not agree with any winning combination shown in FIG. 8,the combination loses, and no payout is made for the loss.

Subsequently, with referring to FIG. 12, a description will be furnishedas to the sub game started if a combination obtained during theaforementioned base game is one in which three “CHANCE” symbols 92 arerearranged on the payline L. When the sub game starts, one of varioustypes of sub games is first selected by lottery. For example, thisembodiment employs five types of sub games of a “shuffle card game”, a“spot the difference”, a “horse racing game”, a “memory” and a “quiz”,as shown in FIG. 12. The sub games give individually different winningconditions and losing conditions to a player, and employ the differentchallenge levels imposed on the player to satisfy the respective winningconditions. Moreover, the various types of sub games each are executedin accordance with input operations by the player.

In addition, as shown in FIG. 9, a lottery result of the sub game isdisplayed by using a scroll area 93 on the main liquid crystal panel 11Bimmediately after the start of the sub game. Specifically, the gamenames of the targeted five types of sub games are displayed, in turn, ina scrolling manner in the scroll area 93, and the game name of a subgame selected by lottery is finally stopped and displayed in the scrollarea 93.

Hereinafter, the sub game is described by taking, as an example, a casewhere the “shuffle card game” is selected as the sub game. FIGS. 10 and11 are diagrams showing game screens displayed on the main liquidcrystal panel 11B in a case where the “shuffle card game” is selected asthe sub game. When the “shuffle card game” is executed, three cards 94to 96 are displayed below the display windows 15 to 17 on the mainliquid crystal panel 11B. One of the three cards 94 to 96 is a “winningcard” on which characters “WIN” are drawn, and the other two cards are“losing cards” on which nothing is drawn. The three cards 94 to 96 areturned upside down so as to be indistinguishable from each other, thenare shuffled, and thereafter, are arranged in a line as shown in FIG.10. Then, the player selects one card among the arranged three cards 94to 96 by using the touch panel 18. As a result, when the player picksthe “winning card” having the characters “WIN” drawn thereon as shown inFIG. 11, the player wins. On the other hand, when the player picks the“losing card” having nothing drawn thereon, the player loses. At thistime, a win/lose display portion 97 displays both the number of times ina case where the player satisfies the winning condition, and the numberof times in a case where the player satisfies the losing condition. Oncethe player satisfies the winning condition three times, the sub game iscompleted and the free game is executed instead of the base game. Atthis time, the number of times of the free game is determined based onthe game outcome of the sub game. For example, in the “shuffle cardgame”, the number of times of the free game is changed according to thenumber of picked cards required to be picked by the player to satisfythe winning condition three times. In the case where the playersatisfies the winning condition by tree trials, four trials and fivetrials, the player is allowed to play the free game 20, 10 and 5 times,respectively. On the other hand, in the case where the player satisfiesthe losing condition three times, the sub game is terminated and thebase game is continuously executed.

Hereinafter, a main control program executed in the slot machine 1according to this embodiment will be described in detail with referringto the drawings. FIG. 13 is a flowchart of the main control program.

First, when a power switch is turned on (power is on), the controller 41activates the main control board 71 and the sub-control board 72, andthen, performs initialization processing in step (hereinafter,abbreviated as S) 1. In this initialization processing, the main CPU 42executes a BIOS stored in the ROM 44. More specifically, the main CPU 42expands, into the RAM 43, compressed data incorporated in the BIOS, andthen, executes the BIOS expanded in the RAM 43 as well as diagnoses andinitializes various peripheral devices. In addition, the main CPU 42writes the game program and other programs from the ROM 44 to the RAM43, and obtains data for payout rate setting and country identificationinformation. Moreover, the main CPU 42 also performs authenticationprocessing for each program during the execution of the initializationprocessing.

Thereafter, at S2, the main CPU 42 reads the game program and the otherprograms from the RAM 43, and performs main game processing by executingthese programs. In the slot machine 1 according to this embodiment, thegame is executed by performing this main game processing. Then, the maingame processing is repeatedly executed while power is supplied to theslot machine 1.

Next, sub-processing for S2 in the above-mentioned main game processingwill be described based on FIG. 14. FIG. 14 is a flowchart of the maingame processing program in the slot machine 1 according to thisembodiment. Incidentally, each of the programs shown below in FIGS. 14and 15 is stored in the ROM 44 or the RAM 43, and is executed by themain CPU 42.

As shown in FIG. 14, at S11, first, the main CPU 42 performs startaccepting processing. At the time of this start accepting processing, aplayer inserts coins and performs the bet operation using the BET buttonof the operation buttons 26. In addition, the main CPU 42 causes each ofthe display windows 15 to 17 in the main liquid crystal panel 11B tobecome transparent or maintain the transparent state by transmitting acontrol signal to the sub-control board 72.

Thereafter, at S12, the main CPU 42 determines whether or not the startbutton of the operation buttons 26 is depressed. This determination ismade based on a signal inputted to the main CPU 42 in response to thepress of the start button. Here, when the start button is not depressed(S12: NO), the routine reverts to the start accepting processing (S11)again. Thereby, the player is allowed to perform an operation forcorrecting the bet amount or the like. On the other hand, when the startbutton is depressed (S12: YES), the main CPU 42 subtracts the bet amountset in accordance with the above bet operation, from the credit amountcurrently owned by the player, and stores the bet amount as betinformation in the RAM 43.

After that, at S13, the main CPU 42 performs symbol lottery processingfor the base game to select symbols to be arranged in the main liquidcrystal panel 11B. More precisely, through the execution of the firstlottery program stored in the RAM 43, the main CPU 42 samples randomnumber values from numeric values within a predetermined range of randomnumbers, and determines symbols (in other words, the stop positions ofthe reels 5 to 7) to be arranged on the payline L by using the sampledrandom number values and the symbol weighting data.

Next, at S14, the main CPU 42 performs reel rotating processing.Specifically, the main CPU 42 causes the motor drive circuit 52 to driveeach of the motors M1, M2 and M3, thereby causing each of the reels 5 to7 to start rotating. After that, the main CPU 42 determines effectpatterns for a unit of the game (patterns for displaying images on themain liquid crystal panel 11B, for outputting sounds form the speaker 31and so on), and causes the sub-control board 72 and the like to startthe effect in accordance with the determined effect patterns byinstructing the sub-control board 72 and the like. Thereafter, uponarrival of a predetermined timing of stop when each of the reels 5 to 7stops rotating, the main CPU 42 performs reel stop processing, therebycausing each of the reels 5 to 7 to stop via the control of the motordrive circuit 52 in accordance with the code number stored in the RAM43. In this way, the combination of symbols determined at S13 mentionedabove is rearranged on the payline L in the main liquid crystal panel11B.

Then, at S15, the main CPU 42 determines whether or not the combinationof symbols arranged on the main liquid crystal panel 11B is agreed withany winning combination to which a predetermined prize is to be awarded.This determination is made based on the code numbers or the like, of therespective reels 5 to 7 stored in the RAM 43.

As a result, when it is determined that the combination is one of thewinning combinations (S15: YES), the routine proceeds to S16. On theother hand, when it is determined that the combination is not any of thewinning combinations (S15: NO), the main game processing is terminated.Note that, when the game is continuously started as the next game, theprocessing following S11 is performed again.

At S16, the main CPU 42 notifies the player of a type of an establishedwinning combination and the content of its prize, by displaying these onthe main liquid crystal panel 11B. For example, as shown in FIG. 7, whenthree “BELL” symbols 91 are displayed on the payline L under thecondition of a bet amount of 2, the characters “BELL×3” are displayed onthe main liquid crystal panel 11B. In addition, 16, which is a numberequivalent to a credit amount to be paid out, is also displayed at thepayout amount display portion 19.

Subsequently, at S17, the main CPU 42 determines whether or not a starttrigger for the sub game is established. Specifically, the start triggerfor the sub game is determined as being established if three “CHANCE”symbols 92 are rearranged on the payline L at the main liquid crystalpanel 11B.

As a result, when the start trigger for the sub game is determined asbeing established (S17: YES), the routine proceeds to the processing forthe sub game (S18). Note that, the processing for the sub game will bedescribed later in detail by using FIG. 15. On the other hand, when thestart trigger for the sub game is determined as not being established(S17: NO), the routine proceeds to S22.

Then, at S19, the main CPU 42 determines whether or not the playersatisfies the winning condition a predetermined number times or more(for example, three times or more) in the sub game executed inaforementioned S18. Here, the winning conditions for the player differamong the types of executed sub games as shown in FIG. 12. For example,when the “shuffle card game” is selected as the sub game, the playerwins if the player picks the “winning card” having the character “WIN”drawn thereon from among multiple cards displayed on the main liquidcrystal panel 11B, as shown in FIG. 11. Instead, when the “spot thedifference” is selected as the sub game, the player wins if the playerspots a point different between two images displayed on the main liquidcrystal panel 11B. Alternatively, when the “horse racing game” isselected as the base game, the player wins if the player spots a winnerof a horse race, among multiple racing horses displayed on the mainliquid crystal panel 11B. Otherwise, when the “memory” is selected asthe sub game, the player wins if the player makes up a pair by turning,a one-by-one basis, two cards displayed on the main liquid crystal panel11B. Alternatively, when the “quiz” is selected as the sub game, theplayer wins if the player selects a correct choice as an answer to aquestion displayed on the main liquid crystal panel 11B.

When it is determined that the player satisfies the winning conditionthe predetermined number of times or more (S19: YES), a determination isfirstly made as to the number of times in a case where the free game isto be executed (S20). Here, the number of times of the free gamedetermined at S20 mentioned previously is based on the game outcome ofthe sub game executed at S18 mentioned previously. For example, when thesub game is the “shuffle card game”, the number of times of the freegame changes according to the number of cards required to be picked bythe player to satisfy the winning condition three times. To be moreprecise, when the player satisfies the winning condition by tree trials,four trials and five trials, the player is allowed to play the free game20, 10, and 5 times, respectively.

Then, after the number of times of the free game is determined, theroutine proceeds to free game processing (S21), whereby the game mode isswitched from the base game to the free game. In the free gameprocessing, the symbol lottery processing and reel rotating processingare successively and repeatedly executed, without requiring any gamingvalue to be spent, the number of times determined in S20 mentionedpreviously. During the free game, if the winning combinations areestablished, the prizes based on the respective winning combinations(see FIG. 8) are cumulatively added up. Incidentally, the symbolweighting data used for selecting a symbol by lottery during the freegame may be the same as that of the base game, or alternatively, may beone allowing the winning combinations to be established with a higherpossibility. On the other hand, when it is determined that the playerdoes not satisfy the winning condition the predetermined number or moretimes (S19: NO), the routine proceeds to S22 without executing the freegame.

Then, at S22, the main CPU 42 pays out, to the player, the prize that isbased on the established winning combination. Here, when the CASHOUTbutton in the operation buttons 26 is depressed, the credit amount canbe paid out as coins (1 credit is equivalent to 1 coin) corresponding tothe credit amount, or can be paid out as a barcode-attached ticket. Notethat, when the free game is executed, the prizes cumulatively added upduring the free game are collectively provided to the player.

Next, sub-processing for S18 of the aforementioned sub game processingwill be described based on FIG. 15. FIG. 15 is a flowchart of asub-processing program of the sub game processing in the slot machine 1according to this embodiment.

First, at S31, the main CPU 42 performs lottery processing for selectingone sub game among the various types of sub games. Specifically, themain CPU 42 selects one of the five types of sub games shown in FIG. 12,by executing the second lottery program included in the game program. Inaddition, the main CPU 42 executes the third lottery program, therebysetting various kinds of parameters needed to execute the selected subgame.

Then, at S32, the main CPU 42 displays, on the main liquid crystal panel11B, a game screen based on the sub game selected at S31 mentionedabove, and proceeds with the sub game based on the game screen displayedon the main liquid crystal panel 11B. Incidentally, the sub game isexecuted in accordance with player's input operations received throughthe touch panel.

Thereafter, at S33, the main CPU 42 determines whether or not the playersatisfies the winning condition in the sub game. Here, the winningconditions for the player differ among the types of executed sub gamesas shown in FIG. 12. The challenge levels imposed on the player tosatisfy the respective winning conditions also differ among the types ofsub games.

Then, when it is determined that the player satisfies the winningcondition (S33: YES), the number of times in a case where the playersatisfies the winning condition is counted (S34). When the number oftimes in a case where the player satisfies the winning condition iscounted a predetermined number of times (for example, three times), thesub game is terminated. In contrast, when it is determined that theplayer does not satisfy the winning condition (S33: NO), the routineproceeds to S35.

In addition, at S35, the main CPU 42 determines whether or not theplayer satisfies the losing condition in the sub game. Here, the losingconditions for the player differ among the types of executed sub gamesas shown in FIG. 12.

Thereafter, when it is determined that the player satisfies the losingcondition (S35: YES), the number of times in a case where the playersatisfies the losing condition is counted (S36). When the number oftimes in a case where the player satisfies the losing condition iscounted a predetermined number of times (for example, three times), thesub game is terminated. In contrast, when it is determined that theplayer does not satisfy the losing condition (S35: NO), the routineproceeds to S37.

At S37, the main CPU 42 determines whether or not a condition forterminating the sub game is satisfied. As for the slot machine 1according to this embodiment, the condition for terminating the sub gameis determined as being satisfied when the number of times in a casewhere the player satisfies the winning condition or the number of timesin a case where the player satisfies the losing condition reaches apredetermined number of times (for example, three times). Instead, acondition where a predetermined time elapses after the start of the subgame may be employed as the condition for terminating the sub game.Otherwise, the condition for terminating the sub game may be a conditionwhere a total sum of the number of times in a case where the playersatisfies the winning condition and the number of times in a case wherethe player satisfies the losing condition reaches a predetermined numberof times (for example, four times).

Then, when the condition for terminating the sub game is determined assatisfied (S37: YES), the sub game is terminated and the routineproceeds to the aforementioned determination processing at S19.Thereafter, as described above, when it is determined that the playersatisfies the winning condition the predetermined number of times ormore, the free game is executed after switching from the base game. Onthe other hand, when the condition for terminating the sub game isdetermined as not being satisfied (S37: NO), the routine returns to S33.

As has been described above, in the slot machine 1 according to thisembodiment, when the base game is started, all the reels 5 to 7 startrotating, and the symbols are arranged on the main liquid crystal panel11B after the predetermined time has elapsed (S14). At this time, if thearranged symbols form the combination in which three “CHANCE” symbols 92are arranged on the payline L (S17: YES), the sub game, which isdifferent from the base game, is executed during the base game (S18).Then, if the player satisfies the winning condition the predeterminednumber of times of more in the sub game (S19), the game mode is switchedfrom the base game to the free game, and then, the free game is executed(S21). Accordingly, the condition for starting the free game may bevariously changed without being limitative to a game outcome of the basegame. In addition, the player is allowed to play the sub game inaddition to the base game, thus avoiding monotony of the game. Thisenables the player to continue playing the game for a long time, thusenhancing the entertainment of the game. In addition, the free game isstarted when it is determined that the player satisfies the winningcondition the predetermined number of times of more in the sub game, andthis promotes player's expectations for the start of the free game withthe progress of the sub game. Moreover, during the base game, the subgame is executed when a combination including the particular symbols(“CHANCE” symbols 92) is arranged on the main liquid crystal panel 11Bin the base game. This also promotes player's expectations for an eventwhere the particular symbols are arranged in the base game. Further,since there are multiple types of sub games, the executed sub game ischanged for every session of the sub game, thereby avoiding monotony ofthe game. Moreover, the condition for switching to the free game canalso be changed for every session of the sub game, so that theentertainment of the game is enhanced. Additionally, the multiple typesof sub games employ the different challenge levels to be imposed on theplayer to satisfy the respective winning conditions, whereby the playerfeels a different level of expectations depending on the type of theselected sub game. Hence, the slot machine 1 provides the player withsuch a different level of expectations, depending on the type of theselected sub game, thereby enhancing the entertainment of the game.Furthermore, the slot machine 1 is capable of providing the game thatlets even a player with a poor gaming technique enjoy playingsufficiently and prevents a player with a good gaming technique fromgetting bored.

In addition, the game outcome of the sub game is used as a base fordetermining the number of times of the free game executed subsequentlyto the sub game (S20). Thus, according to the game outcome of theexecuted sub game, the player feels a different level of expectations ofacquiring a large amount of gaming values in the subsequently-executedfree game. Accordingly, the entertainment of the game is enhanced.

It should be noted that the present invention is not absolutelylimitative to the aforementioned embodiment, but can be improved ormodified without deviating from the essence of the present invention.For example, in this embodiment, when the three particular symbols(“CHANCE” symbols 92) are arranged on the payline L during the basegame, the sub game is executed. However, the condition for executing thesub game may be another condition. For example, the sub game may beexecuted when the arranged symbols includes at least one particularsymbol (“CHANCE” symbol 92). Otherwise, the sub game may be executed,like a mystery bonus, no matter what symbols are arranged.

Moreover, in this embodiment, the free game is executed when the playersatisfies the winning condition the predetermined number of times ofmore during one session of the sub game. Nevertheless, the number oftimes in a case where the player satisfies the winning condition may beaccumulated over several sessions of the sub game, and the free game maybe executed when the cumulative number of times reaches a predeterminednumber of times or more. In other words, a player gradually satisfies acondition for executing the free game by playing several sessions of thesub game.

Furthermore, the slot machine 1 of this embodiment is a slot machine forthe slot game using three mechanical reels, but may be one for a slotgame using 5 or 9 reels. Instead, the slot machine 1 may also be a slotmachine using video reels.

1. A slot machine comprising: a display adapted to have a plurality ofsymbols arranged on the display; a bet receiving button configured toreceive a bet operation; and a controller configured to execute a basegame and a free game by switching these games under predeterminedconditions, the base game being designed to start in response to aconsumption of gaming values equivalent to a bet amount received by thebet receiving button, and to award a prize when the plurality of symbolsarranged on the display forms a predetermined combination, the free gamebeing designed to start without requiring any gaming value to beconsumed, and to award a prize when the plurality of symbols arranged onthe display forms a predetermined combination, wherein the controller isconfigured to execute a sub game different from the base game during thebase game, and to switch a game mode from the base game to the free gamein response to a game outcome of the sub game.
 2. A slot machinecomprising: a display adapted to have a plurality of symbols arranged onthe display; a bet receiving button configured to receive a betoperation; and a controller configured to execute a base game and a freegame by switching these games under predetermined conditions, the basegame being designed to start in response to a consumption of gamingvalues equivalent to a bet amount received by the bet receiving button,and to award a prize when the plurality of symbols arranged on thedisplay forms a predetermined combination, the free game being designedto start without requiring any gaming value to be consumed, and to awarda prize when the plurality of symbols arranged on the display forms apredetermined combination, wherein the controller is configured toexecute a sub game different from the base game during the base game; todetermine whether a player satisfies a winning condition a predeterminednumber of times of more in the sub game; and to switch a game mode fromthe base game to the free game when the controller determines that theplayer satisfies the winning condition the predetermined number times ormore.
 3. A slot machine comprising: a display adapted to have aplurality of symbols arranged on the display; a bet receiving buttonconfigured to receive a bet operation; and a controller configured toexecute a base game and a free game by switching these games underpredetermined conditions, the base game being designed to start inresponse to a consumption of gaming values equivalent to a bet amountreceived by the bet receiving button, and to award a prize when theplurality of symbols arranged on the display forms a predeterminedcombination, the free game being designed to start without requiring anygaming value to be consumed, and to award a prize when the plurality ofsymbols arranged on the display forms a predetermined combination,wherein the controller is configured to execute a sub game differentfrom the base game when a predetermined combination including aparticular symbol is arranged on the display during the base game; todetermine whether or not a player satisfies a winning condition for thesub game a predetermined number of times of more; and to switch a gamemode from the base game to the free game when the controller determinesthat the player satisfies the winning condition for the sub game thepredetermined number of times or more.
 4. The slot machine according toclaim 1, wherein the controller is configured to execute the sub gamedifferent form the base game when a combination including a particularsymbol is arranged on the display during the base game.
 5. The slotmachine according to claim 1, wherein when a predetermined condition issatisfied during the base game, the controller is configured to selectone sub game among a plurality of types of sub games and executes theselected sub game.
 6. The slot machine according to claim 1, wherein thesub game includes a plurality of types of sub games, and the pluralityof types of sub games have different challenge levels from each other,the challenge levels imposed on a player to satisfy winning conditionsof the respective sub games.
 7. The slot machine according to claim 1,wherein the controller is configured to determine the number of times ofthe free game to be executed subsequently to the sub game, on the basisof a game outcome of the sub game, and to execute the free game thedetermined number of times.